1. Field of the Invention
The present invention generally relates to computer software. More specifically, the present invention relates to techniques for guiding semi-automatic quantity takeoff data from computer aided design drawings.
2. Description of the Related Art
The term computer aided design (CAD) generally refers to a broad variety of computer-based tools used by architects, engineers, and other construction and design professionals. CAD applications may be used to construct computer models representing virtually any real-world construct. Commonly, CAD applications are used to compose computer models and drawings related to construction projects. For example, a CAD application may be used to compose a three-dimensional (3D) model of a house or an office building. Once composed, these CAD models are often used to generate a variety of two-dimensional (2D) and 3D views such as plan, profile, section, and elevation views. Additionally, such models may be used to generate architectural, construction, engineering, and other documentation related to the construction project.
A common requirement of construction projects is to generate an estimate of the cost of the project from the building drawings. This estimate can then be used as part of the bidding process or as part of the pricing process. The term “quantity takeoff” is generally referred to as process of estimating the quantities of materials needed to construct a project based on the project drawings and specifications. The quantities involved in quantity takeoff may include numerical counts, such as the number of doors and windows in a project, but may also include other quantities such as the volume of concrete or the lineal feet of wall space. The rest of the cost estimate of a project entails determining the types of materials that will be used as well as the unit costs of those materials.
Today, the quantity takeoff process is typically performed manually. For example, a project manager may use a printout, a pen, and a clicker to manually count objects depicted in a set of construction documents. The project manager may physically mark each instance of an object in a CAD drawing, using the clicker to maintain an instance count. A digitizer is often used for taking measurements from the printout. The project manager or cost engineer evaluates each drawing element individually, identifies the material associated with the element, identifies and quantifies the appropriate dimension of the element, calculates the element cost, and adds the element cost to the overall cost estimate.
One drawback to this approach is that it has proven to be error-prone. Also, this approach is both labor intensive and time consuming. Moreover, if the project design is modified after the original cost estimate is calculated, the takeoff process may need to be repeated. If the takeoff process is not repeated after design changes, accumulated inaccuracies in the cost estimate may adversely affect the bidding or pricing process. Another drawback to the manual approach is that it is difficult and expensive to accurately assess the cost impact of different design choices.
As the foregoing illustrates, what is needed is a more effective and flexible technique for estimating the cost of a construction project and, more particularly, for generating quantity takeoff data.